FIU Bridge Collapse

Update April 16, 2018:  The NTSB could take a full year or longer.   See link:

For NTSB investigators piecing together FIU bridge collapse, ‘evidence tells the story’

When the NTSB  investigation of the March 16 collapse  is complete, it will be posted here.

I think one of  the best summary is from Wikipedia as follows:

Wikipedia: FIU Pedestrian Bridge Collapse

I found interesting that this is functionally, it was more of a truss bridge than a cable stayed bridge, and that truss bridges constructed of concrete are very rare.  Also, the statement,  “The bridge was meant to last more than 100 years, and to withstand a Category 5 hurricane, in a statement by the university.[27]”  will undoubtedly be re-examined by experts.

Scientific American: How Do Forensic Engineers Investigate Bridge Collapses, Like the One in Miami?

A lot of engineers have joined the discussion of the bridge collapse, as follows:

Eng-tips

The engineering discussion is limited.  NTSB investigators have much more vital information including the  “as built” schematics and notes on design changes.

There are parts 1 to 4 – search the site for more details.

Updates:

Miami Herald: Two weeks ago, FIU’s bridge abruptly collapsed. Here’s what we know so far

The failed span  lacked redundancy with just a single set of supporting beams.   Truss bridges normally have two sets, one on either side.  The unusual design of the criss-crossing beams going down the center, gave pedestrians  unobstructed views, but added to the vulnerability of the bridge to failure.

NTSB discloses new details about work performed before FIU bridge collapsed

News stories can be found through Google searches.  Here are a few recent ones:

3/22/2018:   Who had ultimate control of the project?  Florida Department of Transportation had “oversight responsibility” but considers this to be a FIU project.

3/22/2018:  Two construction company  teamed up to construct the bridge:  Figg Engineering Group and Munilla Construction Management (MCM).   Media reports have identified violations of code by both companies in the past construction projects:

MH: Meet MCM and FIGG, the two firms behind FIU’s collapsed pedestrian bridge

3/21/2018:  First Lawsuit Filed After Miami Bridge Collapse

Note: it is common for lawyers to seek out victims of accidents, and file initial documents for legal action before the accident has been properly investigated.   These filing are very preliminary.

FIU held a vigil in memory of the victims of the bridge collapse on March 21, 2018.  After the vigil, students marched to the intersection of 107 Avenue and 8th Street, within site of the accident.  (Various media reports).

_____

Six motorists died in this tragic accident.  This page may be more of interest for individuals trying to understand how the accident happened rather than other aspects of the accident.  I’ll add to it from time to time.

In general, the diagrams can be clicked on to enlarge in a separate window.

The video shows the accident began near the north pylon, which was followed by collapse of the entire span.   It occurred almost exactly where the crane is shown positioned above the canopy.  I have added some blue lines, to make it clearer.   This frame is at the 8 second mark.   The entire collapse occurred in about 2 seconds.  The video was taken from a car going in the east direction, so the collapse is at the north end of the span.

Youtube video of the collapse

video showing break

The link below, provides the engineering drawings  from the original proposal, dated September 30, 2015,  from pages 103 to 115.

MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015

The north pylon, which I called the tower post is shown below.   The top of the pylon is 20 x 21 ft. At the base, the pylon is 10 x 6 ft.    Below surface, the foundation is 5-ft thick.

However,.  there may have been design changes, as the top of the pylon looks more rectangular than square. I think this is the top of the north pylon.

top of pylon

 

One engineer (AvE) has  focused on the PT bars which may have snapped once the truss was in position.     Additional stress was put on the north end of the truss, as one transporter was further away from the end of the truss.     See Youtube video:

A very good analysis of the accident

He also makes an excellent point, as accidents of this type (failure during installation) are very rare, because it is easy to over design (make a bridge  stronger than required) to overcome imperfections and/or  slight errors in design.

The frame from the car cam shows  the accident began at support members 10 and 11.  This drawing  is the perspective of the bridge going in the west direction, with the south end to the left.

tension bars

 

The installation does not appear to have followed plan, as the transporter was moved further away from the north pylon.

So, it seems more that the accident began in the north end of the span.   CBS news states the bridge was already behind schedule and over budget, due to design changes.  The north pylon was moved 11-ft to the north,  moving it very close to the canal (see link below).

I will update this as more information is made public.   There must be a thousand internet postings, so I can not possibly post everything.  My interest lies more in the engineering aspects of the accident.   See links below:

Links:

Florida bridge collapse: Design change put project behind schedule, millions over budget